<?php

/**
 * Class GF256
 *
 * @created      16.01.2021
 *
 * @author       ZXing Authors
 * @author       Smiley <smiley@chillerlan.net>
 * @copyright    2021 Smiley
 * @license      Apache-2.0
 */
declare(strict_types=1);

namespace zxf\QrCode\Common;

use zxf\QrCode\QRCodeException;

use function array_fill;

/**
 * This class contains utility methods for performing mathematical operations over
 * the Galois Fields. Operations use a given primitive polynomial in calculations.
 *
 * Throughout this package, elements of the GF are represented as an int
 * for convenience and speed (but at the cost of memory).
 *
 *
 * @author Sean Owen
 * @author David Olivier
 */
final class GF256
{
    /**
     * irreducible polynomial whose coefficients are represented by the bits of an int,
     * where the least-significant bit represents the constant coefficient
     */
    //	private int $primitive = 0x011D;

    private const logTable = [
        0, // the first value is never returned, index starts at 1
        0,   1,  25,   2,  50,  26, 198,   3, 223,  51, 238,  27, 104, 199,  75,
        4, 100, 224,  14,  52, 141, 239, 129,  28, 193, 105, 248, 200,   8,  76, 113,
        5, 138, 101,  47, 225,  36,  15,  33,  53, 147, 142, 218, 240,  18, 130,  69,
        29, 181, 194, 125, 106,  39, 249, 185, 201, 154,   9, 120,  77, 228, 114, 166,
        6, 191, 139,  98, 102, 221,  48, 253, 226, 152,  37, 179,  16, 145,  34, 136,
        54, 208, 148, 206, 143, 150, 219, 189, 241, 210,  19,  92, 131,  56,  70,  64,
        30,  66, 182, 163, 195,  72, 126, 110, 107,  58,  40,  84, 250, 133, 186,  61,
        202,  94, 155, 159,  10,  21, 121,  43,  78, 212, 229, 172, 115, 243, 167,  87,
        7, 112, 192, 247, 140, 128,  99,  13, 103,  74, 222, 237,  49, 197, 254,  24,
        227, 165, 153, 119,  38, 184, 180, 124,  17,  68, 146, 217,  35,  32, 137,  46,
        55,  63, 209,  91, 149, 188, 207, 205, 144, 135, 151, 178, 220, 252, 190,  97,
        242,  86, 211, 171,  20,  42,  93, 158, 132,  60,  57,  83,  71, 109,  65, 162,
        31,  45,  67, 216, 183, 123, 164, 118, 196,  23,  73, 236, 127,  12, 111, 246,
        108, 161,  59,  82,  41, 157,  85, 170, 251,  96, 134, 177, 187, 204,  62,  90,
        203,  89,  95, 176, 156, 169, 160,  81,  11, 245,  22, 235, 122, 117,  44, 215,
        79, 174, 213, 233, 230, 231, 173, 232, 116, 214, 244, 234, 168,  80,  88, 175,
    ];

    private const expTable = [
        1,   2,   4,   8,  16,  32,  64, 128,  29,  58, 116, 232, 205, 135,  19,  38,
        76, 152,  45,  90, 180, 117, 234, 201, 143,   3,   6,  12,  24,  48,  96, 192,
        157,  39,  78, 156,  37,  74, 148,  53, 106, 212, 181, 119, 238, 193, 159,  35,
        70, 140,   5,  10,  20,  40,  80, 160,  93, 186, 105, 210, 185, 111, 222, 161,
        95, 190,  97, 194, 153,  47,  94, 188, 101, 202, 137,  15,  30,  60, 120, 240,
        253, 231, 211, 187, 107, 214, 177, 127, 254, 225, 223, 163,  91, 182, 113, 226,
        217, 175,  67, 134,  17,  34,  68, 136,  13,  26,  52, 104, 208, 189, 103, 206,
        129,  31,  62, 124, 248, 237, 199, 147,  59, 118, 236, 197, 151,  51, 102, 204,
        133,  23,  46,  92, 184, 109, 218, 169,  79, 158,  33,  66, 132,  21,  42,  84,
        168,  77, 154,  41,  82, 164,  85, 170,  73, 146,  57, 114, 228, 213, 183, 115,
        230, 209, 191,  99, 198, 145,  63, 126, 252, 229, 215, 179, 123, 246, 241, 255,
        227, 219, 171,  75, 150,  49,  98, 196, 149,  55, 110, 220, 165,  87, 174,  65,
        130,  25,  50, 100, 200, 141,   7,  14,  28,  56, 112, 224, 221, 167,  83, 166,
        81, 162,  89, 178, 121, 242, 249, 239, 195, 155,  43,  86, 172,  69, 138,   9,
        18,  36,  72, 144,  61, 122, 244, 245, 247, 243, 251, 235, 203, 139,  11,  22,
        44,  88, 176, 125, 250, 233, 207, 131,  27,  54, 108, 216, 173,  71, 142,   1,
    ];

    /**
     * Implements both addition and subtraction -- they are the same in GF(size).
     *
     * @return int sum/difference of a and b
     */
    public static function addOrSubtract(int $a, int $b): int
    {
        return $a ^ $b;
    }

    /**
     * @return GenericGFPoly the monomial representing coefficient * x^degree
     *
     * @throws \zxf\QrCode\QRCodeException
     */
    public static function buildMonomial(int $degree, int $coefficient): GenericGFPoly
    {

        if ($degree < 0) {
            throw new QRCodeException('degree < 0');
        }

        $coefficients = array_fill(0, ($degree + 1), 0);
        $coefficients[0] = $coefficient;

        return new GenericGFPoly($coefficients);
    }

    /**
     * @return int 2 to the power of $a in GF(size)
     */
    public static function exp(int $a): int
    {

        if ($a < 0) {
            $a += 255;
        } elseif ($a >= 256) {
            $a -= 255;
        }

        return self::expTable[$a];
    }

    /**
     * @return int base 2 log of $a in GF(size)
     *
     * @throws \zxf\QrCode\QRCodeException
     */
    public static function log(int $a): int
    {

        if ($a < 1) {
            throw new QRCodeException('$a < 1');
        }

        return self::logTable[$a];
    }

    /**
     * @return int multiplicative inverse of a
     *
     * @throws \zxf\QrCode\QRCodeException
     */
    public static function inverse(int $a): int
    {

        if ($a === 0) {
            throw new QRCodeException('$a === 0');
        }

        return self::expTable[(256 - self::logTable[$a] - 1)];
    }

    /**
     * @return int product of a and b in GF(size)
     */
    public static function multiply(int $a, int $b): int
    {

        if ($a === 0 || $b === 0) {
            return 0;
        }

        return self::expTable[((self::logTable[$a] + self::logTable[$b]) % 255)];
    }
}
